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VM_PAGE_BITS(9) FreeBSD Kernel Developer's Manual VM_PAGE_BITS(9)

vm_page_bits, vm_page_set_validclean, vm_page_clear_dirty, vm_page_set_invalid, vm_page_zero_invalid, vm_page_is_valid, vm_page_test_dirty, vm_page_dirty, vm_page_undirty
manage page clean and dirty bits

#include <sys/param.h>
#include <vm/vm.h>
#include <vm/vm_page.h>
vm_page_bits(int base, int size);
vm_page_set_validclean(vm_page_t m, int base, int size);
vm_page_clear_dirty(vm_page_t m, int base, int size);
vm_page_set_invalid(vm_page_t m, int base, int size);
vm_page_zero_invalid(vm_page_t m, boolean_t setvalid);
vm_page_is_valid(vm_page_t m, int base, int size);
vm_page_test_dirty(vm_page_t m);
vm_page_dirty(vm_page_t m);
vm_page_undirty(vm_page_t m);

vm_page_bits() calculates the bits representing the DEV_BSIZE range of bytes between base and size. The byte range is expected to be within a single page, and if size is zero, no bits will be set.
vm_page_set_validclean() flags the byte range between base and size as valid and clean. The range is expected to be DEV_BSIZE aligned and no larger than PAGE_SIZE. If it is not properly aligned, any unaligned chunks of the DEV_BSIZE blocks at the beginning and end of the range will be zeroed.
If base is zero and size is one page, the modified bit in the page map is cleared; as well, the VPO_NOSYNC flag is cleared.
vm_page_clear_dirty() clears the dirty bits within a page in the range between base and size. The bits representing the range are calculated by calling vm_page_bits().
vm_page_set_invalid() clears the bits in both the valid and dirty flags representing the DEV_BSIZE blocks between base and size in the page. The bits are calculated by calling vm_page_bits(). As well as clearing the bits within the page, the generation number within the object holding the page is incremented.
vm_page_zero_invalid() zeroes all of the blocks within the page that are currently flagged as invalid. If setvalid is TRUE, all of the valid bits within the page are set.
In some cases, such as NFS, the valid bits cannot be set in order to maintain cache consistency.
vm_page_is_valid() checks to determine if the all of the DEV_BSIZE blocks between base and size of the page are valid. If size is zero and the page is entirely invalid vm_page_is_valid() will return TRUE, in all other cases a size of zero will return FALSE.
vm_page_test_dirty() checks if a page has been modified via any of its physical maps, and if so, flags the entire page as dirty. vm_page_dirty() is called to modify the dirty bits.
vm_page_dirty() flags the entire page as dirty. It is expected that the page is not currently on the cache queue.
vm_page_undirty() clears all of the dirty bits in a page.

None of these functions are allowed to block.

This manual page was written by Chad David <>.
December 1, 2001 FreeBSD 12.0-RELEASE

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